1. Field of the Invention
The present invention relates to gas-passage plates of a solid polymer electrolyte type fuel cell.
2. Description of the Related Art
With regard to the configuration of this type of fuel cell, a pair of catalyst-carrying gaseous diffusion electrodes are overlaid on both main surfaces of an ion-conductive solid polymer electrolyte membrane (hereinafter, referred to as a solid electrolyte membrane), thereby producing a power generating cell. In order to obtain a desired voltage output by connecting a plurality of these single power generating cells in series, the plurality of power generating cells are stacked with a separator interposed between neighboring two power generating cells. In this case, the separator has electric conductivity and functions as a current collector of two diffusion electrodes disposed on both the sides of the separator.
When a fuel gas and an oxidation gas are respectively supplied on both the sides of the separator so as to supply the fuel gas and the oxidation gas to respective gaseous diffusion electrodes, ionic conduction proceeds at solid electrolyte membranes and chemical reactions proceed at the respective gaseous diffusion electrodes. A voltage is thereby generated between a pair of gaseous diffusion electrodes, and output to an outside circuit through a pair of separators which are disposed on both ends and serve as current collectors. In generating power, how uniformly the supply gases are supplied on electrode surfaces of the gaseous diffusion electrodes determines gas utilization ratios, and directly affects power generating efficiency and output performance.
However, when the supply gases are supplied to the entire surfaces of the gaseous diffusion electrodes, there are no contact areas of the separators and the gaseous diffusion electrodes, and accordingly it becomes difficult to collect a generated electric current efficiently and remove heat generated at the gaseous diffusion electrodes. Therefore, at boundary portions of the separators and the gaseous diffusion electrodes, channels are formed so as to restrict the flow directions of the supply gases, and certain ratios of contact areas of the separators and the gaseous diffusion electrodes are secured. Since these channels are generally formed on the separators, the separators will be referred to as gas-passage plates hereinafter in this specification. All types of separators including a separator comprised of a plurality of component parts will be referred to as gas-passage plates.
By the way in the above fuel cells, in order to make ion conductivity of the solid electrolyte membranes exhibited fully and to keep power generating efficiency high, the supply gases (the fuel gas and the oxidation gas) are humidified and water vapor concentrations are increased in the supply gases.
Moreover, the solid polymer electrolyte-type fuel cells function to convert the energy of the electrochemical reaction of hydrogen and oxygen forming water into electrical energy, water is produced at the cathode. (Depending on the type of membrane, a certain liquid is produced at the anode.)
Consequently, in the above channels for the supply gases, a large amount of water generated from the reaction is contained in the downstream, especially on the outlet side, and there is a fear that liquidified water fills the gas channels and causes flooding.
In order to prevent the supply gases from stagnating due to the reaction-generated water, various types of gas channels have been proposed, as disclosed in the publications of Japanese Unexamined Publication (KOKAI) Nos. H6-215,780, H6-96,781, and H6-86,730. The gas channels disclosed in these publications are roughly classified into three types. In the first type the contact surfaces of one gas-passage plate and one electrode are regularly dotted and the gas passages have the shape of a lattice. The second type includes gas passages and contact surfaces arranged in stripes. In the third type the gas passage is a single path extending from an inlet port to an outlet port.
All of these passage types have advantages and disadvantages. The channel in the form of a lattice does not cause flooding, but does not positively allow gaseous diffusion or water discharge. The channel in the form of stripes is simple in structure, but has problems with gas supply and water dischargeability. The channel in the form of a single path secures a high gas flow speed and attains superior gaseous diffusivity, but pressure loss (passage resistance) is increased and accordingly initial pressure at a gas supply apparatus must be increased and the electric power balance sheet of this system does not necessarily improve.